Oculist&#39;s chart



y 1936- A. E. COVELLE 4 ,459

' OCULISTS CHART Filed Juhe 25, 1954 Patented May 19, 1936 UNlTED' STATES RATE??? QFFEQE 4 Claims.

This invention relates to those charts used by oculists and opticians to determine the angularity and degree of astigmatism of a patients eyes. It aims to improve such charts with a View to facilitating the determination of these errors in vision more accurately.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawlo ing, and the novel features will be particularly pointed out in the appended claims.

In the drawing,

Figure 1 is a front elevation of a chart embodying features of this invention;

Fig. 2 is a side elevation of the chart shown in Fig. 1;

Fig. 3 is a vertical, sectional view on the line 3-3, Fig. 1, the parts, however, being shown on a considerably larger scale; and

Fig. 4 is a rear view of certain of the elements of the chart.

The construction shown comprises a circular disk 2, the front face of which bears any suitable number of heavy black radial lines 3 on a white 5 background. As shown, two lines only are used,

these lines being located at right angles to each other and intersecting at the center of the disk.

Surrounding the margin of this disk is a circular head 4 of a supporting stand 5, on which the disk is mounted for rotation about its own center, and the narrow margin of the part 4 is graduated in degrees. So far as these features are concerned, the chart is substantially like those which have been used heretofore.

According to the present invention, the central portion of the chart has a narrow slit 6 formed in it through which a thin beam of light from any convenient source, such as the electric lamp 1, Fig. 2, can pass. Preferably this light is made of some color which contrasts sharply with that of the adjacent black and white or equivalently colored surfaces of the disk, red being preferred. For this purpose the lamp 1 used may have a red bulb. Preferably, however, this color is obtained by securing a thin film of red celluloid 8, Figs. 3 and 4, to the rear surface of the disk 2 immediately behind the slit 6 and using a white source of light. The walls of the slit can be blackened to prevent reflection, and spreading of the rays 1 of the beam. The control of the beam also appears to be facilitated and a more uniform illumination of the slit is produced by using a thin film of celluloid Ill immediately behind the colored film 8. Both films can be secured in place by means of a metal plate l2 provided with a slit 58 of approximately the same width as the slit 6, this plate and the two films of celluloid being all secured in position by four screws, certain of which are shown at M, passing through holesin the part l2 and threaded into the diskZ.

I prefer to mount this disk so that it can be revolved from a remote position, as in the ar rangement shown in my earlier Patent No. 1,850,168, and for this purpose, as well as to facilitate the desired illumination of the slit 6, I mount the disk 2 on a tubular journal l5 which, in turn, is rotatably supported by the cylindrical bearing surface l6, Fig. 3, of the stand 5. For convenience in manufacture, and particularly since it is preferable to make the disk 2 of aluminum or an aluminum alloy, the disk is secured to an annular plate I], as by means of screws lii-l8, and said plates are fastened to the journal i5, which may consist of a section of steel or bronze tubing. Preferably a spacing collar 20, slightly thicker than the stand 5, encircles the tubular journal l5 and provides the desired lateral clearance necessary for easy running. Mounted on the rearward end of the member !5 is a thin pulley 2| to receive the operating cord 22, this pulley usually being made in sections and secured to another spacing collar 23 which is pinned or screwed to the tubular member l5. This provides an easy running construction which can be manufactured'and assembled economically.

In using the apparatus the procedure described in my earlier patent may be followed, particularly if this chart is used in the apparatus there shown. However, the present chart is equally useful alone, or in connection with other astigmatic charts of a common form. Usually the ordinary wheel chart is used in initially determining approximately the axis or meridian of a patients astigmatism. The eyes are, of course, tested one at a time. When the meridian has been determined approximately by the wheel chart, or by the present chart, the disk 2 is set in a corresponding position, at which time one of the lines 3 will appear much blacker to the patient than that at right angles to it. Assuming that this is the line 3 at right angles to the slit 6, and that this slit is at this time illuminated, it will then appear as two or more red lines parallel to each other, the number of these apparent lines depending upon the degree of astigmatic error.

It is assumed that the proper spherical correction has previously been made by a trial lens placed in the test frame on the patients face. If now the chart is rotated to a position 90 from its most distinct. If now the chart is turned exactly from this position, and test lenses having different degrees of cylindrical correction are placed successively in the frame, the blurring or appearance of several red lines can be cleared up. When the exact correction has been made, then the patient will see a single very thin red line, and this line will have the same appearance in all positions of the chart. At this time, also, both the black lines will appear of the same width and degree of blackness. This thin illuminated slit, however, has proved to be especially useful in determining the power of the cylindrical lens required to correct the astigmatic error. It is also useful in improving the accuracy of determination of the axis of the astigmatism. If the astigmatic error is very substantial, then when the chart is in the position in which the series of red lines appears at each side of the slit 6, the black line 3 at right angles to this slit will seem to divide each of these lines into two red lines located, respectively, above and below the black line extending through them. This will be the appearance when the transverse black line is on the correct axis or meridian. Any change now made in the position of this axis or meridian in either direction away from this position will seem to have the effect of blotting out the division between the apparent red lines so that they will appear continuous instead of being divided. This fact is very useful in determining the astigmatic axis or meridian with a high degree of accuracy in those cases in which extreme accuracy is most important.

In order to obtain the best results I have found that the slit 6 should be made extremely narrow, preferably between five and ten-thousandths of an inch in width. Some advantages of the invention can be obtained, however, with greater widths up to, say, in the neighborhood of thirtythousandths, or even somewhat above this figure. Its length is not so important so long as it is made substantial, but it should be at least a half inch in length if the apparatus is used in the ordinary manner when the patient sits about twenty feet away from it. I prefer to make the slit about one and a. quarter or one and a half inches in length. There appears to be some advantage, also, in breaking the line in the middle, as by securing a small metal piece 24, Fig. 3, at this point so as to avoid any interruption of the black line 3 which intersects the red line 6. The fact that this slit preferably is made so thin introduces a problem in manufacture which I have found can be conveniently overcome by making the disk in two semi-circular sections, the line of division being lengthwise of and passing through the center of the slit 6. This permits the cutting of half the width of the slot out of each section, after which the two sections can be brought together on the supporting annulus I1 and secured to it by these screws I 8| 8.

While I have herein shown and described a preferred embodiment of my invention, it will be understood that the invention may be embodied in other forms without departing from the spirit or scope thereof.

Having thus described my invention, what I desire to claim as new is:

1. An astigmatic chart having heavy black radial lines on a white background, means supporting said chart for rotation, a narrow slit in said chart for permitting the passage therethrough of a thin beam of light, said slit being located centrally in the chart and in line with one of said black lines, another of said black lines intersecting said slit at the center of the chart, means for directing rays of light through said slit and for controlling said rays, the beam of light transmitted through said slit contrasting sharply in color with that of both said lines and said background.

2. An astigmatic chart having a narrow slit for the passage therethrough of a thin beam of light, a tubular journal, a bearing cooperating with said journal to support said chart for rotation, said slit being radially located with reference to the axis of rotation and at the end of the bore in said tubular journal, a source of light arranged to direct its rays through said bore and said slit, parts associated with said slit to maintain the rays of light transmitted through it in approximately a parallel relationship, and said slit being surrounded by a relatively large chart area comprising a white background having heavy black radial lines on it, said slit being in line with one of said black lines and lying at right angles to another.

3. An astigmatic chart having heavy black radial lines on a white background, means supporting said chart for rotation, a narrow slit in said chart for permitting the passage therethrough of a thin beam of light, said slit being located centrally in the chart, and in line with one of said black lines, means for directing rays of light through said slit and cooperating with said slit to so control the rays of light that to a person of normal vision in viewing the slit from a normal testing distance it appears like an extremely thin, sharply defined, straight line of a color contrasting sharply with that of both said black lines and said white background.

4. An astigmatic chart having radial lines of one shade and a background of a contrasting shade, and a narrow slit in line with one of said radial lines for the passage therethrough of a thin beam of light, means for supporting said chart for rotation, said slit being less than tenthousandths of an inch in width, and radially located in the chart and at least half an inch in length, whereby its angular position can be adjusted by such rotation, means associated with said chart to designate its different angular positions, means for directing rays of light through said slit, said rays of light contrasting sharply in color with that of the adjacent area of the chart, and said slit and the parts associated with it to direct and control said rays being constructed and arranged to prevent any substantial spreading of said rays that have passed through the slit.

' ALBERT EUGENE COVELLE. 

